1. Field of Invention
The present invention relates to a fan rotation speed control circuit, and more particularly to a fan rotation speed control circuit, applicable for controlling the rotation speed of the fan according to a loading state of a power supply system.
2. Related Art
The current power supply standard of the server can be classified into two types, namely, ATX power supply and SSI power supply, in which the ATX power supply standard is mainly applied to desktop computers, work stations, and low-level servers; the SSI power supply standard is mainly applied to servers in various levels.
As the increasing of the processing speed of the computer, the required power also increases, and thus, the power supply system requires a better heat dissipation device for dissipating heats, so as to operate normally in a safe temperature range. A commonly used heat dissipation device is a fan, which is controlled to operate correspondingly through sensing the temperature change of the power supply system. However, the process for sensing a temperature has a defect, that is, after the power supply system has operated for a period of time, the temperature of the system rises or drops along with the changing of the loading state, and at this time, a temperature sensing circuit senses the change of the temperature, thereby outputting a signal to a fan rotation speed control circuit to control the fan rotation speed to be adjusted correspondingly. In other words, due to the time required for sensing the temperature, this fan rotation speed controlling process generates delay in controlling the fan rotation speed, instead of controlling the fan rotation speed in real time according to the loading state, and thus it still needs to be improved.
With reference to Taiwan Patent No. M290192, a fan control circuit is disclosed, which includes a heat conductive circuit and a feedback control circuit. The feedback control circuit includes a driving portion for supplying a current to the fan, the heat conductive circuit converts the change of the ambient temperature into electric signals, and the feedback control circuit generates a control signal through calculation. The control signal controls the driving current supplied to the fan by the driving portion, thereby controlling the rotation speed of the fan.
Although the above patent can control the rotation speed of the fan according to the temperature in the computer case, to ensure the temperature in the computer case be kept within an allowable range, thereby saving the power consumption of the system, and reducing the noises in the computer case. However, similar to the fan rotation speed control circuit in the temperature sensing mode, it still has the delay problem in the control of the fan rotation speed.
Therefore, in the fan rotation speed control circuit of the current power supply system, the method of controlling the fan rotation speed by means of sensing the temperature has the problem of time delay, which cannot control the fan rotation speed in real time according to the loading state. Moreover, the specification and type of the power supply provided by the power supply system cannot satisfy the requirements of other circuits.